Solvent extraction of oil



June 7, 1949. c. M. STONE SOLVENT EXTRACTION OF OIL 2 shets-sneet 1Filed May 7, 1947 SNN@ INVENTOR. CHA LES/VZ TONE ATHEN/5 Ys June 7,1949. c. M. STONE 2,472,499 soLvENT EXTRACTION oF OIL l Filed May '7,1947 2 Sheets-Sheet 2 IVI ' IN VEN TOR. CH .55 /l/f. TONE )1 TT@ RNE ysPatented June 7, 1949 UNlTED STATES OFFICE SOLVENT EXTRACTION F OILApplication May 7, 1947, Serial No. 746,490

6 Claims.

This invention relates to a method of effecting extraction of oil with asolvent liquid which is at least partially miscible with water atordinary temperatures or which forms with water a minimum boilingazeotrope.

In accordance with this invention, a charge oil such as derived fromcrude petroleum is extracted with a selective solvent liquid such asfurfural so as to form raffinate and extract phases respectively. Thesephases comprising oil and solvent liquid are separately treated toseparate solvent from the raffinate and extract oil fractions. Thistreatment involves distilling the solvent from the oil with the aid ofsteam, thereby obtaining a distillate vapor mixture of solvent andwater. This distillate vapor mixture is passed to an absorption zonewherein it is subjected to countercurrent contact with a non-aqueousabsorption liquid such as gas oil and which is higher boiling than waterunder the conditions prevailing in the absorption zone. As a result ofthis absorptive contact the solvent liquid is absorbed in the absorptionliquid and thus removed from the water vapor, the absorptive treatmentbeing carried out under conditions of temperature and pressure such thatthe water vapor undergoes no substantial condensation. The absorptionliquid containing dissolved oil is removed from the absorption tower andcooled or otherwise treated to effect separation between absorptionliquid and solvent.

The resulting recovered solvent liquid is recycled for use in theextraction zone.

Water vapor is removed from the absorption zone with a compressor orblower and passed at least in part to the aforesaid distilling operationto provide steam for aiding the distillation. Compression of the watervapor stream imparts some superheat to this stream thereby making itmore effective as a distilling medium in the distilling operation.

According to one modification of the invention, all of the water vaporstream removed from the absorption zone is recycled to the distillingoperation preferably after heating.

This is advantageous, since the water vapor stream usually contains asmall amount of residual solvent liquid.

According to another modification, only a portion of the water vaporstream is passed to the distilling operation with provision forsupplying fresh steam thereto. In the latter case, the remaining portionof the water vapor stream is passed to a stripping zone wherein it issubjected to fractional condensation so as to remove a stream of watersubstantially free from residual solvent, which water is discharged fromthe system. From this stripping operation there is obtained a constantboiling mixture of solvent and water which can be recycled to theaforesaid absorption zone.

Heretofore in the extraction of hydrocarbon oil with a selective solventsuch as furfural, it has been customary to subject the resultingraffinate and extract phase to a series of distilling steps involvingvaporization of a portion of the solvent from the oil fractions in theabsence of steam, and stripping of the residual solvent from thesefractions in the presence of steam. The distillate obtained from thestripping operation has been condensed to effect separation of the bulkof the water from the solvent liquid. However, since the solvent andwater are miscible to a substantial extent, the resulting furfural phasecontains a substantial amount of dissolved water while the resultingwater phase retains a substantial amount of dissolved furfural even atthe relatively low temperatures normally prevailing in the condensingequipment. These phases have then been subjected to further distillationin order to recover the furfural.

A feature of the present invention is that it provides a simplifiedsolvent recovery operation and reduces the amount of distillationotherwise required. By the method of this invention all of the solventis distilled from the raffinate and extract oil fractions with the aidof steam. The resulting distillate comprising furfural and water vapor,without intermediate condensation, and preferably with a small amount ofheating, is passed to an absorption tower wherein the solvent isabsorbed from the vapor mixture in an absorption liquid in which thesolvent is soluble while water vapor is substantially insoluble therein.The absorption is performed under temperature and pressure conditionssuch that the water remains in the vapor state. The water vapor fromwhich the solvent has been absorbed is repressured and reheated ifnecessary and then recycled to the previously mentioned distillingoperation. This method of operation avoids loss of the latent heat ofvaporization of the steam.

In order to describe the invention in more detail, reference will now bemade to the figures of the accompanying drawing.

As indicated in Figure I, a charge oil such as a furnace oil or Dieseloil fraction of petroleum is conducted from a source not shown through apipe l to an extraction tower 2, the latter being of the conventionaltype. A selective solvent such arranco 3 as furfural is introduced tothe upper portion of the tower through a pipe 3.

The oil and furfural streams are subjected to countercurrent contact inthe tower 2 at an elevated temperature in the range of about 150 to 200F., so as to eiect separation into ranate and extract phases. I

It will be understood that the oil and furfural streams may bepre-heated to any n'ec'e'ssary degree prior to introduction to theextraction tower, such heating being accomplished in a con; ventionalmanner.

The resulting ranate phase comprising raffinate oil mixed with arelatively small proportion of the solvent liquid is continuouslyreinove'd from the upper portion of the tower through a pipe 5, Whilethe extract phase, comprising the extract fraction of the oil dissolvedin the major proportion of the solvent liquid is continuously drawn oifrom the bottom of the tower` through a pipe 6.

Y"Iiie railnate phase stream is passed to a distilling column 7 whereinthe solvent is fractiona'lly distilled lfrom the 'railinate oil. Areboiler 8 may be provided in the lower portion of the tower and openstream injected into the bottom 'of the tower through a pipe 9.Additional steam i'srinj'ected to lthe lower portion 'of the towerthrough a pipe Il) from a source referred to later. Provision may bemade for supplying reflux to the top 'of the column through a pipe il soas to control the temperature. y

In the usual case, the pressure prevailing at the bottom :of the 'columnmay be ab'o`ut ten lpounds per square inch "gauge while that 'at "thetop of the tower is about 've pounds, reux 'being supplied so as tomaintain 'altemper'ature vat the topof the column of about y225" F.

"-lhe solvent is thus ldistilled from vthe oil, the latter lioeirig'discharged from the bottom of the t'ower through a pipe |2. l

The resulting distillateconiprising furfu'ral and water vapor is removed'through a` pipe I3 which communicates with a pipe -Hl leading to 'aheat Zexchanger '|`5 wherein the 'distillate `vapo`r mix- 'turemay be'raised yto a "temperature 'of about 246 F. The A'distillate Ivapormixture will comprise about y65% by `weight water vapor. It is Vpassedat a pressureof "about five pu'nds gauge, `into the 'lower 4portion ofan ='absorber 2'0 'provided with suitablepacking'alnd Whein it lissubjected 'to countercurrent contact 'with absorbent liquid suchas gasoil. 'A temperature of'abo't l220" F. is maintained "at 'thetop 'of theabsorption 'tower with a pressure substantially atmospheric.

The 'rich absorption oil 4contai'r'iing 'dissolved 'iurfural is drawnoff from 'the bottom f the absorber through a pipe V2| and 'cooler'22,wherein 'it is'coled yt0 a'tenipera'tu'ie falb'u'tBO Ato fl-00F. andpassed to a separator 23 wherein separation 'between oil and vvfufuraloccurs.

The separated furfural retaining a small percent of oil, forexample'abot8`or'10%,`is drawn oir through a pipe 2"4 -andreturned tothe extrac--tion tower through 'pipe '3.` A'water vapo'rstream is drawn'`fromthetopo'f the'absrber'JZU 'through a pipe 25 leading-to the-suction side of acompr'essor or centrifugal 'blower which dischargesinto'a'pipe "25 at 'a 4pressure 'of about :te'n 'pounds 'gauge 'andsuflicient to force the 'vapor back'intothe distillorf'eoiiunuoosiy `ingcolumn l0. 'A portion of this 'repressured vwater ,vapor stream, raisedt`o a temperature of `abo1`1t33`5"'F.-as aresultof 'compressionisc`onducted lthrough ja, pipe '28 bonnecting with pre- LviouslyAmentioned pipe T0, through which "the 4 reheated water vapor isrecycled to the distilling column 1. The remainder of the Vapor streamnot passed to the heater or heat exchanger 2'! is conducted through apipe 30 to the lower portion of a stripper 3|, wherein it is subjectedto fractional distillation, heat being supplied to the bottom of thestripper through a reboiler 32. A temperature of about 225 F. ismaintained at the top of the stripper 3|, which is operated undersubstantially atmospheric pressure. There is discharged from the bottomof the stripper a stream of water substantially free from solvent.

A distillate comprising an azeotropic mixture of furfural and watervapor is removed through 'a pipe 34 connected with pipe I4 and throughwhich the distillate can be returned to the absorber 20. A portion ofthe distillate stream from pipe 34 can be by-passed through a pipe 35and cooler 36 wherein it is condensed and the condensate accumulated ina drum 3l' from which it is returned through a pipe 38 as reilux to thestripper 3|.

Referring now to the extract phase removed from the extraction tower,this phase is con'- ducted through the pipe 6 to a distilling columnlill which is similar to the distilling column 'l previously describedand also operated in a substantially similar manner. In this way thesolvent furfural is stripped from the extract oil which later isdischarged through pipe 4|.

The resulting distillate vapor comprising fur- :f-ural and-steam iscontinuously removed through a -pipe 42 connecting with the previouslymentioned pipe I'l through which it is conducted to the yabsorber 2U.Also as indicated in the drawing, -a portion oi the reheated water vaporstream passing through the pipe 28 may be diverted 'through a branchpipe 43, and so introduced 4to the distilling column GU to provide thesteam required therein.

Referring now to Figure 1I, it will be seen that the extraction tower2,thedistilling columns r"l `and lll), the absorber l2U, the blower 25A,and 'connecting -p'ipes have their counterparts in Figlure I'. Theessential 4distinction in lthe method of ilow illustrated -in Figure IIover Ithat illustrated in Figure I has to do with the treat'-, 'ment ofthe stream 4of absorbent and dissolved soli/'ent after -removal from'the absorber "2U, As shown in Figure II, this stream `is 'drawn "olli.through pipe 2| and introduced directlyto a 'distilling'column 50,wherein the solvent is fractionally distilled from vthe absorbent. The44columnfmay be provided with a `reboiler 5| to supply the necessaryheat for distillation. 'The denuded absorbent at a 'temperature 'abovethe llo'oilingpoint'of thesolventis continuously drawn on 'from the'bottom of 'the column -`5|) through pipe 52 'and a 'heat exchanger 53,wherein it A'is cooled to a'temperature of about 240 F. The cooledabsorbent is conducted through pipe '54 from 'which it is discharged`into 'the top of 'the absorber 2U.

The recovered 'solvent 'is removed as a 4distillate from the top lofthecolumn 550 "at a temperature of about 323 F.`through apipe 55 and'passedthrough a condenser '56 from which Athe condensate is dischargedinto a drum'Bl. Aporftion 'of the v'condensed 'liquid may be returnedthrough pipe "58 as reflux to the top of the 'column 5U. The remainderof the-recovered .solvent 'is 'drawn off through a pipe 59 through whichitis returned to 'thepipe-"S for recycling tofthe extractor '2. Y

In 4the operation illustrated 'in 'Figure II, it

. will be seen that the total eliiuent vapor stream from the top of theabsorber 2D is forced by 40 respectively. In other words, the heatedwater vapor stream discharged from the blower 25-A is used to provideall of the steam required in the distilling columns 'l and ti) so thatprovision for the addition of extraneous steam is unnecessary undersettled operating conditions.

While the invention has been described with special reference to theextraction of a specific mineral oilfraction, nevertheless it iscontemplated that the invention has application when the extraction isapplied to other petroleum fractions, as for example, lubricating oilstocks.

Also, it is contemplated that the invention has application in the caseof extractions carried out on oils other than those derived from amineral source. For example, it may be useful in connection with thesolvent extraction or oils derived from vegetable and animal sources.Selective solvents other than furfural are also contemplated. These mayinclude other derivatives of the fural group and other aldehydes such asbenzaldehyde. Nitro-benzene and ketones such as aliphatic ketones may beused.

In any case, the invention is particularly concerned with the use oforganic solvent liquids which are relatively high boiling and which aremiscible at least to some extent with water and which form azeotropestherewith.

Absorbent liquids other than gas oil may be used in the absorber 29. Theabsorbent liquid may comprise either extract oil or rainate oil obtainedin the extraction operation. It may comprise a portion of the charge oilto the extractor. Advantageously it comprises oil of relativelynon-aromatic character and Which is immiscible with water or hassubstantially no solvent action upon water at the temperaturesprevailing in the solvent recovery operation. It is also contemplatedthat instead of mineral oil the absorbent may comprise a conventionalsolvent liquid which is of substantially different boiling Apoint thanthe selective solvent being used in the extr-actor 2.

If in the treatment of relatively low boiling oils, a small amount ofthe more volatile oil constituents distill over in the azeotrope mixturefrom the column 1, provision may be made for withdrawing such oiliconstituents at a later point in the system. These constituents mayremain, at least in part, in the recovered solvent and be recycledthrough the extraction zone. They may accumulate in part in theabsorption oil, in which case a portion of this stream may be drawn onthrough pipe 21 in Figure I or through pipe 21A in Figure II and beconducted to a suitable still for separation of the volatileconstituents from the absorption medium, the latter being returned tothe system.

Obviously, many modications and variations of the invention, ashereinbefore set forth, may be made without departing from the spiritand scope thereof, and therefore only such limitations should be imposedas are indicated in the appended claims.

I claim:

1. In the fractional separation of oil by extraction with a watermiscible organic solvent liquid wherein a mixture comprising solventliquid and a fraction of said oil is obtained as a result of saidextraction and the solvent is thereafter sep- 'arated fromI said oilfraction with the aid of steam in a distillation zone, thereby obtaininga mixture of solvent and water, the method of recovering solvent fromsaid solvent-water mixture which comprises passing said solvent-watermixtureA to an absorption zone, subjecting it therein to contact with anon-aqueous liquid absorbent for said solvent liquid which is higherboiling kthan water, effecting said contact at a temperature above theboiling point of water at the pressure prevailing within said absorptionzone, separately removing from said zone a vapor stream of watercontaining some residual solvent and a liquid stream of absorbentcontaining dissolved solvent recovering solvent from removed absorbent,recycling a portion of said vapor stream to said distilling zone,passing another portion thereof to a secondary distilling zone, forminga secondary distillate consisting of an azeotropic mixture of solventand water and a secondary residual liquid comprising water, dischargingsaid residual liquid, and recycling said secondary distillate to saidabsorption zone.

2. The method according to claim l in which the organic solvent liquidis furfural.

3. In the fractional separation of oil by extraction with a watermiscible organic solvent wherein a mixture comprising solvent liquid anda fraction of said oil is obtained as a result of said extraction, themethod comprising passing said mixture to a distilling zone,fractionally distilling solvent liquid from the oil in the presence ofadded steam thereby obtaining a mixture of solvent liquid and water,passingresulting solventwater mixture to an absorption zone, subjectingit therein to contact with a non-aqueous liquid absorbent in saidsolvent which is higher boiling than water, effecting said contact at atemperature above the boiling point of water at the pressure prevailingWithin said absorption Zone, separately removing from said zone a vaporstream of water containing some residual solvent and a stream ofabsorbent liquid containing dissolved solvent, passing said vapor streamn part to said distilling zone recovering solvent from said removedstream of absorbent and dissolved solvent, passing another portion ofsaid vapor stream to a secondary distilling zone, forming a secondarydistillate consisting of an azeotropic mixture of solvent and water anda secondary residual liquid comprising water, discharging said residualliquid and recycling said secondary distillate to said absorption zone.

4. The method according to claim 3 in which the organic solvent liquidis furfural.

5. In the fractional separation of oil by extraction with a watermiscible organic solvent liquid, the method comprising subjecting chargeoil and solvent to extraction in an extraction zone, removing from saidextraction zone a fraction of said oil mixed with solvent liquid,passing said mixture directly to a stripping zone, separating solventfrom oil in said stripping zone with the aid of added steam, therebyobtaining a distillate mixture of solvent and water, passing saidsolvent-water mixture directly to an absorption zone, subjecting it tocontact therein with a nonaqueous liquid absorbent for said solvent andwhich is higher boiling than water, effecting said Contact at atemperature above the boiling point y of Water at the pressureprevailing within said absorption zone, separately removing from saidzone a vapor stream of water containing some residual solvent and astream of absorbent liquid containing dissolved solvent, recoveringsolvent from said absorbent, yrecycling recovered solventtoseidextraction Zone, passing said vapor stream in part to said strippingzone to provide added Steam, passing another portion of said vaporstream to a secondary distilling zone, forming a secondary distillateconsisting of an azeotropic mixture of solvent and water and a residualliquid comprising Water, discharged said residual liquid and Irecyclingsaid secondary distillateto said absorption Zone.

6. In the fractional separation of oil by .extraction with furfural, themethod comprising subjecting hydrocarbon oil to extractiva contact withfurfural in an extraction zone, .removing from said zone a fraction ofsaid charge oil-mixed 15 with solvent liquid, passing said fraction.containing solvent liquid directly to a separating zone, distillingfurfural from said oil -fraetion therein with the aid of added steam,thereby obtaining a distillate comprising furfural and water, .passingsaid distillate directly to an absorption zone, subjecting saiddistillate to countercurrent contact therein with a nonaqueous absorbentliquid for said solvent and which is higher boiling than water,effectingr said countercurrent contact at a temperature above theboiling point of Water at the pressure prevailing within said absorption5 liquid from said absorbent, recycling recovered solvent and liquid tosaid extraction zone, passing a portion of said water vapor stream tosaid separating zone to provide added steam therein, passing anotherportion of said vapor stream to a.

10 secondary distilling zone, forming a secondary distillate consistingof an azeotropic mixture of solvent and water and a secondary residualliquid comprising water, discharging said residual liquid and recyclingsaid secondary distillate to said absorption zone.

`GHARLIEIS M. STQNE.

REFERENCES @TED The :.following references are of record in the iile ofthis patent:

UNITEDSTATES PATENTS Number Name Date .2,167,730 Smokey e..,., A118. 11,19.39 25 2,305,248 Fleer et al Dec, 15, l194:2 2,339,786 Larsen et al.Jan. 22, 1944

